refactor: replace Code Index MCP with native CCW CodexLens

Migrate all Code Index MCP references to CCW's built-in CodexLens tool:
- Update context-search-agent with codex_lens API calls
- Update test-context-search-agent with new search patterns
- Update memory/load command file discovery reference
- Update context-gather and task-generate-tdd MCP capabilities
- Update INSTALL docs to reflect CodexLens as built-in feature
- Sync all mirrored files in skills/command-guide/reference/

Old API (mcp__code-index__*) → New API (mcp__ccw-tools__codex_lens)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/commands/workflow/tools/context-gather.md

@@ -237,7 +237,7 @@ Execute complete context-search-agent workflow for implementation planning:
 ### Phase 1: Initialization & Pre-Analysis
 1. **Project State Loading**: Read and parse `.workflow/project.json`. Use its `overview` section as the foundational `project_context`. This is your primary source for architecture, tech stack, and key components. If file doesn't exist, proceed with fresh analysis.
 2. **Detection**: Check for existing context-package (early exit if valid)
-3. **Foundation**: Initialize code-index, get project structure, load docs
+3. **Foundation**: Initialize CodexLens, get project structure, load docs
 4. **Analysis**: Extract keywords, determine scope, classify complexity based on task description and project state
 
 ### Phase 2: Multi-Source Context Discovery